Many medical procedures are performed using minimally invasive surgical techniques, wherein one or more slender implements are inserted through one or more small incisions into a patient's body. With respect to ablation, the surgical implement can include a rigid or flexible structure having an ablation device at or near its distal end that is placed adjacent to the tissue to be ablated. Radio frequency energy, microwave energy, ultrasound energy, laser energy, extreme heat, and extreme cold can be provided by the ablation device to kill the tissue.
With respect to cardiac procedures, a cardiac arrhythmia can be treated through selective ablation of cardiac tissue to eliminate the source of the arrhythmia. A popular minimally invasive procedure, radio frequency (RF) catheter ablation, includes a preliminary step of conventional electrocardiographic mapping followed by the creation of one or more ablated regions (lesions) in the cardiac tissue using RF energy. Multiple lesions are frequently required because the effectiveness of each of the proposed lesion sites cannot be predetermined due to limitations of conventional electrocardiographic mapping. Often, five lesions, and sometimes as many as twenty lesions may be required before a successful result is attained. Usually only one of the lesions is actually effective; the other lesions result in unnecessarily destroyed cardiac tissue.
Deficiencies of radio frequency ablation devices and techniques have been overcome by using cold to do zero degree or ice mapping prior to creating lesions, as taught in U.S. Pat. Nos. 5,423,807; and 5,281,213; and 5,281,215. However, even though combined cryogenic mapping and ablation devices permit greater certainty and less tissue damage than RF devices and techniques, both the cryogenic and the RF devices are configured for spot or roughly circular tissue ablation.
Spot tissue ablation is acceptable for certain procedures. However, other procedures can be more therapeutically effective if multiple spot lesions along a predetermined line, or a single elongate or linear lesion is created in a single ablative step. Radio frequency ablation devices are known to be able to create linear lesions by dragging the ablation tip along a line while it is active. However, no cryogenic devices are known that are optimized for, or which are even minimally capable of, creating an elongate lesion. The deficiency in creating elongate lesions is applicable for flexible, rigid, and semi-rigid catheter and surgical probe type systems. In the former, the method of access is through the blood vessel system and in the latter through a surgical incision in the patient's chest wall.
Additionally, as noted above, the surgical implement can include a rigid or flexible structure having an ablation device at or near its distal end. The rigid or flexible structure can be an elongate, highly-flexible shaft with a steerable distal end for negotiating a path through the body of a patient, as well as a rigid shaft for use in more invasive procedures where a more local opening or direct access to a treatment site is available or created.
While rigid structures or probes may be useful in some applications, they have certain limitations as well. For example, without a shape especially adapted for reaching a particular location in the body of a patient, the rigid nature of the probe limits the area of tissue that can be reached and treated. Even where a relatively large incision is provided, tissue areas that are not at least somewhat directly accessible cannot be reached.
Although a rigid probe can be provided with a predetermined shape, one must select a probe that has the most appropriate shape for positioning the working portion of the probe in contact with the treatment site in view of the particular anatomical pathway to be followed in the patient. It will be appreciated that a large inventory of rigid probes may be required to accommodate the various treatment sites and patient anatomies. Further, for a patient having a relatively uncommon anatomic configuration and/or a difficult to reach treatment site, all rigid probes of an existing set may have less than optimal shapes for positioning. This may impair the prospects of successfully carrying out the treatment procedure, especially when the treatment is one such as an ablation treatment that relies on good tissue contact and operates locally upon the contacted tissue. For an ablation probe which must bear against tissue at the remote region to ablate a lesion, the contour followed by the probe in reaching the target site will in general further restrict the direction and magnitude of the movement and forces which may be applied or exerted on the working portion of the device to effect tissue contact and treatment.
It would, therefore, be desirable to provide a probe that, while having sufficient rigidity to facilitate positioning of the probe to a selected location within the body of a patient, is also better adapted to reach or treat the particular targeted anatomy of the patient.
It would also be desirable to provide a probe having a working portion with sufficient controlled flexibility to conform to curved or irregular tissue surfaces, yet be resistant to kinking, folding or pinching, in addition to having sufficient strength to safely contain high-pressure working fluids.